mon/Paxos: set first_committed on first commit

Signed-off-by: Sage Weil <sage@inktank.com>
mon/Paxos: update first_committed only from paxos

Do not touch the in-memory first_committed until the trim commits.  This
avoids any possible confusion due to races and keeps commit() as similar
to store_state() as possible.

Similarly, do not touch first_committed from store_state.  We should
*only* pull it out of the kv store.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/Paxos: clean up removal of pre-conversion paxos states

Use a helper, independent of trim machinery, and call on leader, too.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/PaxosService: rename scrub

Make the name patch the one in Paxos.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/Paxos: simplify trim()

Collapse all the trim methods into a single simple method.

Signed-off-by: Sage Weil <sage@inktank.com>
mon: do not reopen MonitorDBStore during startup

level doesn't seem to like this when it races with an internal compaction
attempt (see below).  Instead, let the store get opened by the ceph_mon
caller, and pull a bit of the logic into the caller to make the flow a
little easier to follow.

    -2> 2013-06-25 17:49:25.184490 7f4d439f8780 10 needs_conversion
    -1> 2013-06-25 17:49:25.184495 7f4d4065c700  5 asok(0x13b1460) entry start
     0> 2013-06-25 17:49:25.316908 7f4d3fe5b700 -1 *** Caught signal (Segmentation fault) **
 in thread 7f4d3fe5b700

 ceph version 0.64-667-g089cba8 (089cba8fc0e8ae8aef9a3111cba7342ecd0f8314)
 1: ceph-mon() [0x649f0a]
 2: (()+0xfcb0) [0x7f4d435dccb0]
 3: (leveldb::Table::BlockReader(void*, leveldb::ReadOptions const&, leveldb::Slice const&)+0x154) [0x806e54]
 4: ceph-mon() [0x808840]
 5: ceph-mon() [0x808b39]
 6: ceph-mon() [0x806540]
 7: (leveldb::DBImpl::DoCompactionWork(leveldb::DBImpl::CompactionState*)+0xdd) [0x7f363d]
 8: (leveldb::DBImpl::BackgroundCompaction()+0x2c0) [0x7f4210]
 9: (leveldb::DBImpl::BackgroundCall()+0x68) [0x7f4cc8]
 10: ceph-mon() [0x80b3af]
 11: (()+0x7e9a) [0x7f4d435d4e9a]
 12: (clone()+0x6d) [0x7f4d4196bccd]
 NOTE: a copy of the executable, or `objdump -rdS <executable>` is needed to interpret this.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/PaxosService: add post_paxos_update() hook

Some services need to update internal state based on other service's
state, and thus need to be run after everyone has pulled their info out of
paxos.

Backport: cuttlefish
Signed-off-by: Sage Weil <sage@inktank.com>
mon/PGMonitor: use post_paxos_update, not init, to refresh from osdmap

We do two things here:
 - make init an one-time unconditional init method, which is what the
   health service expects/needs.
 - switch PGMonitor::init to be post_paxos_update() which is called after
   the other services update, which is what PGMonitor really needs.

This is a new version of the fix originally in commit
a2fe0137946541e7b3b537698e1865fbce974ca6 (and those around it).  That is,
this re-fixes a problem where osds do not see pg creates from their
subscribe due to map_pg_creates() not getting called.

Backport: cuttlefish
Signed-off-by: Sage Weil <sage@inktank.com>